mmap intro

example_set_one.py

import mmap
with open("hello.txt","wb") as f:
    f.write(b"Writing")

f = open("hello.txt","r+b")
mm = mmap.mmap(f.fileno(),0)
print(mm.readline())
#Output: b'Writing'
print(mm[:5])
#Output: b'Writi'

mm[5:] = b"a7"
# we cannot exceed the allocated bytes
# so if I add some extra bytes 
mm[5:] = b"writing extra bytes"

"""
---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
 in 
      3 
      4 # so if I add some extra bytes
----> 5 mm[5:] = b"writing extra bytes"
      6 mm.close()

IndexError: mmap slice assignment is wrong size
"""
mm.close()
---------------------------------------------------------------------------------------------------------------------------
#To map anonymous memory, -1 should be passed as the fileno along with the length.
# Using with the with statement

import mmap
with mmap.mmap(-1,20) as mm:
    mm.write(b"Hello Worlllld")